Dangerous Points Research Articles

Dynamic characteristics of wave entry for a deep-sea mining vehicle: Numerical and experimental studies

The deep-sea mining vehicle (DSMV) experiences complex impacts upon the wave entry, which directly affects the safety and reliability of the whole deployment system. In this paper, a computational fluid dynamics (CFD) method is proposed to investigate hydrodynamic properties and wave-entry effects of a DSMV with varying laying speeds. Firstly, a fifth-order Stokes surface gravity wave simulating Sea State 4 conditions is constructed based on the volume of fluid (VOF) method. Then, the overset mesh scheme is utilized to establish the multiple degree-of-freedom (DOF) model of DSMV which bears the traction loads of laying cable. Laboratory prototype tests are conducted, and the captured results of cavitation evolution and motion properties corroborate the present model. Numerical results indicate that the DSMV entering the wave danger point will experience hydrodynamic forces several to dozens of times greater, severely threatening structural safety. During the wave entry process, two phases of nonlinear deceleration occur, posing a risk to the umbilical cable. Surge and pitch motions caused by waves and structural asymmetry may lead to deployment position deviation. Based on the trends observed in the simulation data, guidance for deployment operations has been proposed.

Fatigue Strength Analysis of Rail Fastening Baseplate

Superstructural elements of a railway track experience dynamic loads varying over time. As a consequence, this is accompanied by the initiation and accumulation of fatigue damages. Defects in intermediate rail fastening are quite difficult to identify using flaw detection methods, and some can be destructed. In particular, rail fastening baseplates often fail due to insufficient fatigue strength.Purpose: To investigate the fatigue strength of rail fastening baseplate.Methodology: Development of the mathematical model of deformation based on the finite element method (FEM). Strength analysis of the baseplate using the model of a variable-thickness slab resting on a nonlinear elastic foundation. The latter is modeled by a set of rods with nonlinear deformation and parameters determined by compression tests of the baseplate. A mathematical model developed in COSMOS software for the FE analysis of the stress-strain state of the baseplate at a time-varying load from rolling equipment and assembly forces from attaching the baseplate to the sleeper and rail.Research findings: The cyclic loading parameters are obtained at dangerous points of the baseplate and its durability is analyzed at different loads with respect to unevenness of track settlement and failure of bolt connections of rail fasteners. The influence of these factors on actual loads on the rail fastener is determined. It is found that the service life of the baseplate mainly depends on the dynamic load.

Influence of geometric factors on cyclic durability of rotor main parts of the hot section of aircraft engines. Validation using lumen control results

A study was conducted of the influence of some geometric factors on such parameters as the position of dangerous points determining the cyclic durability of a part, and the values of cyclic durability at these points. Based on the results of the validation carried out using the results of non-destructive testing and fractographic studies of opened cracks in the main part with operational defects, the adequacy - the degree of compliance with the research results - of the calculation models used to determine the cyclic durability was established. The work was carried out as part of the task of determining the resource indicators of the main part, taking into account the presence of an initial defect.

Simulation Analysis and Experimental Investigation on the Fluid–Structure Interaction Vibration Characteristics of Aircraft Liquid-Filled Pipelines under the Superimposed Impact of External Random Vibration and Internal Pulsating Pressure

This paper investigated the fluid–structure interaction vibration response of an aircraft liquid-filled pipeline under external random vibration and internal pulsating pressure. First, the fluid–structure interaction solution is theoretically analyzed, and the advantages and disadvantages of the direct coupling method and the separation coupling method are compared, with the latter chosen as the simulation analysis method in this study. Second, taking the U-shaped oil pipeline of an aircraft engine as an example, simulation modeling was performed to compare and analyze the fluid–structure interaction vibration response of aircraft liquid-filled pipelines under different working conditions, obtaining the vibration response characteristics of stress danger points under various conditions. Finally, a test bench for an aircraft liquid-filling pipeline was built to explore the influence of external random vibrations with different kurtoses, different pipe wall thicknesses and different working conditions on the vibration response danger points of aircraft liquid-filling pipelines, verifying the simulation conclusions and providing a basis for aircraft liquid-filling pipeline design.

Effect on the physical field of the die during the backward extrusion process of magnesium alloy wheel

The eccentric placement of billets reduces the service life of the dies, and at the same time causes the scrapping of the wheel blanks. However, for axisymmetric forgings, eccentric placement is unavoidable. In this study, the mutual effects between the billet and the die during backward extrusion of magnesium (Mg) alloy wheels are analyzed by physical and numerical simulations, focusing on the effects on the physical field of the die. There were dangerous points in the design of the combined die structure and the lower mating surface of the female die and the bottom die were prone to stress concentration during the filling process of the Mg wheel, which led to the cracking of the die. The eccentric extrusion of the wheel resulted in a slope in the filling height of the rim, and it had a great effect on the physical field and microstructure distribution at the same time, which in turn affected the physical field distribution of the wheel die, resulting in uneven load distribution at the lower rim of the die and reducing the life of the combined die. The combined die structure optimization solution can process the female die into a curved surface along the fracture surface and at the same time process a hollow circular table to cooperate with the bottom die and the female die.

Reliability analysis of the solidification cooling of solid rocket motor grain material.

The reliability of solid rocket motor grain structure during solidification cooling is analyzed. First, a three-dimensional parametric modeling of the grain is carried out by ANSYS finite element software. The dangerous point and dangerous moment can be obtained based on the transient and dynamic thermo-structure coupling under the cooling condition. Moreover, the maximum equivalent strain and temperature values are extracted. Second, a dual neural network model is established based on the probability distribution of the copula function and specific parameters. Finally, the instantaneous reliability during the solidification cooling process of the grain is calculated. Then, the dynamic reliability analysis is realized. The proposed method reduces the computational cost of dynamic reliability of grain structure, demonstrating its applicability in practical engineering problems. Furthermore, comparing the results of the proposed method with the MCS method demonstrates that the proposed method has high computational accuracy.

Prediction of engine combustion chamber outlet temperature field based on deep Learning: Application in aero-engine life extension control

One of the current research hotspots is the prediction of combustion chamber flow field based on deep learning methods, but how to effectively utilize these prediction results is a key issue that needs to be addressed urgently. This paper further proposes a study on the predictive control method for engine life extension considering the dangerous point temperature of turbine guide vane based on the prediction of combustion chamber outlet temperature field. Firstly, a combustion chamber outlet temperature distribution prediction model is established through Computational Fluid Dynamics (CFD) numerical simulation and inception deconvolution network, and integrated into the variable cycle engine component level model to achieve real-time prediction of combustion chamber outlet temperature distribution. Furthermore, based on this, the dangerous point temperature of the high-pressure turbine (HT) guide vanes is introduced as a constraint into the prediction optimization, and a predictive control method for engine life extension considering the thermal mechanical fatigue life (TMFL) of the guide vanes is proposed. The simulation results show that compared to the traditional LEC control method, the temperature at the critical point of the blade is reduced by 12.28 K, and the TMFL of the blade is increased by 29.23 %. The research results of this article provide a good application example for predicting the temperature distribution at the outlet of the combustion chamber, expanding the application scenarios for predicting the flow field parameters inside the engine.

Probabilistic fatigue life prediction of notched specimens based on modified stress field intensity method under multiaxial loading

In practical engineering components, due to the existence of non-uniform stress and strain field near the notch, it brings severe challenges to fatigue life prediction when evaluating the integrity of notched components. In this study, a probabilistic fatigue life prediction model for notched specimens was established by coupling the stress field intensity (SFI) method and Weibull distribution. Firstly, the position of the dangerous point is determined by finite element calculation, and the maximum strain energy density plane through the dangerous point is defined as the critical plane. Secondly, from the perspective of 2D features, the traditional SFI method is modified based on the stress distribution on the critical plane, and a new concept of effective stress is proposed to predict the fatigue life of notched specimens by the experimental data of smooth specimens. Finally, a new non-proportional additional hardening factor is established to characterize the influence of material properties and loading path on fatigue life. The experimental data of Q345 low alloy steel and GH4169 nickel base alloy are used to compare and analyze the proposed model. The results show that the predicted life of the proposed model is in good agreement with the experimental life.

Risk analysis of critical control points of Staphylococcus aureus in layer farms and chicken egg distributors.

Microbiological criteria play a role in verifying the critical control points (CCP), which become part of the hazard analysis, and the CCP system that guarantees quality, considering possible danger points or stages in the food production chain. Studies about Staphylococcus aureus in chicken eggs more extensively discuss the path, source, and level of prevalence of contamination at the final distributor or consumer. Therefore, this study investigates CCP contamination of S. aureus in chicken eggs and their potential consumption, which could endanger human health from the layer farm until the final distributor. This study is critical in health, public health, and veterinary medicine for preventing and controlling consumers' security. This study done for CCP on the chain distribution of chicken eggs starts with preparing production and distribution process flow diagrams for livestock, agents/wholesalers, and retailers. Confirmation of operational production in the field/location study is based on the flow chart that has been arranged, identifying all potential dangers associated with each stage and analyzing potential risks considering every action for controlling identified hazards. The next step involves pinpointing the CCP to counteract the identified threat. An application tree decision defines the CCP, and the logical and final approach is the determination limit critical to the CCP. Analysis results in the determination of CCP contamination of S. aureus, indicating that chicken eggs, personal hands (farm workers, wholesalers, and retailers), shelf eggs, and feces are CCP on farms.

Unique Operating Conditions Analysis of Turboshaft Engines Based on Nonlinear Integrated Model

The unique mission of the helicopter compared to the fixed-wing aircraft introduces challenges to the aerodynamic stability of the turboshaft engine. Thus, the assessment of the availability of stability margin for special operating conditions in the envelope of this equipment is required to guarantee flight safety. In this paper, a rapid nonlinear complete engine method is developed to investigate the effect of helicopter ground-effect operation and high-altitude hovering on aerodynamic stability by considering factors including inlet distortion and component matching. Research indicated that the most dangerous point of stability margin in a unique section of the flight envelope is high altitude hovering, with about a 16.7% reduction in available stability margin compared to standard ground test conditions. This paper also investigates the effects of typical helicopter ground effects on a turboshaft engine and shows that the stability margin will be reduced by a maximum of 1.43% in hovering if the influence of ground effects in the flight envelope is not considered in the design.

Stability Evaluation Method of High Fill Loess Foundation Based on Numerical Simulation

In order to understand the stability evaluation method of high fill loess foundation, the author proposes a study on the stability evaluation method of high fill loess foundation based on numerical simulation. The author first established a three-dimensional finite element model of a multi-level high fill slope using PLAXIS 3D software based on a loess high fill slope engineering project in a certain section of northwest China. The study investigated the effects of changes in fill materials, fill boundaries, slopes, and unloading platforms on slope stability. Secondly, based on the vertical and horizontal displacement of the top and foot of each level of slope under step-by-step filling, the distribution pattern of the most dangerous points of each level of slope and the overall deformation trend of the slope were analyzed. The results indicate that the cohesion and internal friction angle of the filling material are key factors affecting the stability of high fill slopes. Reducing the height of the steps at the boundary between the filling and the undisturbed soil, deepening the width of the steps, reducing the slope, and widening the unloading platform can all improve the stability of the slope. During the construction of lower slopes, there is a significant vertical displacement mutation, while the horizontal displacement mutation is relatively slow; After the construction is completed, the deformation situation is good, and the vertical and horizontal displacement of the higher slope during construction changes greatly, with uneven distribution; After the completion of construction, the consolidation settlement period is long and the deformation is large; Emphasis should be placed on strengthening deformation monitoring at high altitudes after construction is completed. Finally, the platform width can be selected within this range based on the actual engineering situation. After the platform width is greater than 3.6m, as sufficient platform width has been reached at this point, further increasing the platform width has little impact on the safety factor, and the curve gradually flattens out. The research results have determined the stability influencing factors, deformation trends, and development laws of loess high fill slopes in the northwest region, providing a scientific basis for further research on deformation control of loess high fill slopes.

Molecular dynamics simulation of spall behavior of amorphous/crystalline composites under shock loading

The industrial application of metallic glass (MG) is greatly limited due to its poor ductility and susceptibility to catastrophic fracture. The mechanical properties of MG can be effectively improved by adding crystal phases to make amorphous/crystalline composites. Meanwhile, spallation is a typical form of dynamic failure of materials under shock loading. However, the spall behavior of amorphous /crystalline composites has been rarely studied. In this work, the shock induced spallation process of Cu50Zr50/copper (Cu) composite materials was investigated through molecular dynamics (MD) simulations. It is found that stress waves transmit and reflect at interface due to the mismatch of acoustic impedance. Besides, MG is “softer” than the single crystal Cu from the perspective of stress wave propagation. By changing the loading direction, it was found that classical spall is more likely to occur in the Cu phase, while micro-spall is more likely to occur in the MG phase. However, as the loading velocity increases, the spall form in the Cu phase will also transform into micro-spall. The spall strength and strain rate through acoustic approximation and MD simulations were also obtained. Finally, it was observed that the tensile stress superposition region caused by interface reflection waves may form new danger points where spallation may initiate, thereby resulting in complex spall phenomena in composite materials. The conclusions obtained reveal the characteristics of the spall phenomenon in Cu50Zr50/Cu composite materials, which is beneficial to further understanding the spall mechanism and providing guidance for designing amorphous/crystalline composite materials under shock loading.

Noise Pollution Assessment, Spatial Noise Mapping and Associated Health Impacts in Dinajpur City, Bangladesh

Noise pollution is one of the more prevalent types of pollution caused mainly by urbanization. It is characterized as noise propagating throughout a living being in a way that is to its physical and mental health. Along with the growth of the city, trade, business, shopping, education, and other activities have been accelerating. The main purpose of the study was to address the dangerous point of noise pollution in Dinajpur municipality and identify the causes of noise pollution. For this study, data sets on the amount of noise pollution at 35 different places throughout Dinajpur city have been analyzed. Three shifts of data collection were conducted: morning (8 am to 10 am), afternoon (12 pm to 2 pm) and evening (4.00 pm-6.00 pm). Using the ArcGIS 10.8 program, descriptive statistics tools and analysis of variance were carried out. The highest average noise level (105.7 dB) was found at Central Bus Terminal at the time of evening which is a mixed zone. The lowest average noise level (64 dB) was found at Chotogurgola and Balubari at the time of morning and evening respectively which is residential zone. The noise levels throughout the city vastly exceed both the WHO and DoE recommendations. The main causes of noise pollution are the expanding urban area, unregulated auto rice mills establishment, the heavy use of construction equipment, automobile engines, uncontrolled horns, and outrageous auto rickshaws etc. It is vital to take action to lower noise levels because prolonged exposure to noise has numerous negative effects. The development of comprehensive land use plans for this city would benefit from taking noise pollution into consideration.

Smith machine squats pose high risk to ACL graft integrity after the ACL reconstruction and conventional squats are a safer alternative.

The purpose of this study was to evaluate the impact of squats after the anterior cruciate ligament (ACL) reconstruction on the ACL graft, considering new data on biomechanics, posterior tibial slope (PTS)and anterolateral ligament (ALL). Utilising finite element analysis on the new 14-component knee joint model, we have evaluated stresses on the knee elements separately for the knee with a native double-bundle ACL and with a single-bundle ACL graft for the 5° and 14° PTS variants during both conventional and Smith machine horizontal squats. Replacing a native ACL with a single-bundle graft causes an overstrain on the graft compared to the intact ACL under all conditions. Stresses on the ACL, ACL graftand ALL are much higher during the Smith machine squats compared to the conventional ones. The stress on the menisci is 3.6-4.9 times higher with conventional squats. PTS at the squats' lowest point minimally affects ACL stress but impacts menisci. The single-bundle ACL reconstruction (ACLR) does not reproduce the biomechanics of the native ACL and increases stresses in most knee joint elements, according to the current study. Conventional squats are relatively safe for the ACL graft at their lowest point. Passing the half-squat position is the most dangerous point. Smith machine horizontal squats produce stress on the ACL graft several times higher than its estimated breaking load and dangerous stress levels on the ALL. During the rehabilitation following ACLR, it is advisable to prioritise the conventional squats over Smith machine squats until ligamentisation is complete. Level III.

Stress, damage, and fatigue performance analysis of CFRP/Al double-sided countersunk riveted joints with variable rivet-hole clearance

The CFRP/Al countersunk rivet joints are one of the most fatigued dangerous points of the aircraft fuselage. To deeply investigate the failure mechanisms of the riveted joint structures, this paper utilizes electromagnetic riveting technology to prepare single-lap joint specimens and investigates the quasi-static tensile and fatigue failure behaviours of the joints under different rivet-hole clearances and stress levels. In addition, to assist this investigation, a three-dimensional finite element model, combining riveting and fatigue loading, is developed. This model takes into account the strain rate effects during riveting process and progressive failure behavior of various typical damage modes in CFRP laminates. The results indicate that Aluminum alloy sheets fracture dominates the fatigue failure of the joints. Increasing the clearance can reduce the stress amplitude on the shear plane and further enhance the fatigue life of the joints. Furthermore, all additional CFRP damage during the loading process is the growth of the initial riveting damage, and the damage-induced fibre bearing capacity decrease is considered the reason for the increase in stress amplitude of the Al sheet. Last, excessive clearance enlargement does not appreciably diminish the initial riveting damage, instead, it could result in a joint strength reduction.

Effect of Training of Adolescents on Household Environmental Safety from Childhood Injuries in a Rural Area of Delhi.

The environment poses an important risk in the causation of injuries in children. Simple measures in improving the safety of the domestic and peri-domestic environment can go a long way in preventing injuries. This study was conducted to assess the effect of training of the adolescents in the families, on the household environmental safety regarding childhood injuries. A pre- and post-intervention study was conducted over 16 months, on 116 families of two villages of Delhi. Data were collected regarding domestic and peri-domestic environments along with danger points with respect to injuries, of the enrolled houses, during the pre- and post-intervention phases of 4 months each. The intervention comprised training of the eldest adolescent of the family, on causes of common injuries and role of environment in injury causation. Scores were assigned to all relevant aspects, and the total environmental safety scores were calculated. The comparison was made between pre- and post-intervention scores of the two areas. Environmental safety scores were more than 70% in both areas at the baseline with no difference between the two areas. In the intervention area, there was statistically significant improvement of scores after the intervention, in the domestic environment and danger signs within the houses. Training adolescents about the prevention of injuries and motivating them to remain vigilant over domestic environment are effective in bringing about significant change in the household environment with regard to safety from injuries in children. Repeated visits by health workers also increase awareness and change the household environment making it safer for children.

Research on ice shedding and broken conductor in tower-line system based on CR method

In cold climates, the damage to the transmission tower-line system is usually caused by ice shedding, broken conductors, and broken ground wires. To replicate the ice shedding and broken conductor scenarios more accurately and expeditiously within the transmission tower-line system, we have engineered a finite element computational program leveraging the co-rotational theory method, utilizing the C++ programming language. Additionally, we have orchestrated its visualization interface utilizing the QT and Visualization Toolkit (VTK) platforms. This program can accurately and rapidly simulate large displacement geometric nonlinear problems. An ice detachment criterion considering the resultant acceleration is proposed. Compared with previous judgment criteria, the criterion proposed in this article can adapt to the previous prediction accuracy and is more efficient in calculation. A finite element method for disconnection simulation of “node failure” was proposed, and its accuracy and computational efficiency were verified by comparison with experiments. By analyzing the coupling effect of disconnection and deicing in the tower line system, it is concluded that ground wires often have a stronger deicing effect than conductors. Although broken conductor will cause large-scale ice shedding from the span, the impact on the most dangerous point of the tower will be very small, this providing a theoretical basis for ice-covered broken conductor in the tower-line system. The simulation method proposed in this article also provides a new research idea for the simulation of ice shedding and broken conductor of tower-line systems.

Numerical Calculation of Static Strength Performance of Planar Gate Structures

As an important part of the ecological environment, rivers provide an important guarantee for the production and life in China. At present, domestic and foreign for the construction of the gate has been gradually shaped, hydraulic steel gate gradually developed as a hydroelectric power station high head, flood discharge flow of large gate type, the smooth opening and closing of the gate is related to the entire water conservancy hub and downstream of the safety of the residents' lives. For the safety of plane gate, this paper adopts Ansys software to establish a finite element model of plane gate, and calculates the most dangerous point stress of plane gate by considering its most unfavourable loading condition. At the same time, the service life of the allowable stress reduction was considered. The analysis results show that the planar gate meets the strength safety. The main beam is simplified into slender beam and thin-walled deep beam, and the calculation formula of slender beam in the mechanics of materials and thin-walled deep beam in the literature is used to calculate the positive bending stress in the mid-span cross-section of the main beam of the gate, and a comparative analysis is carried out with the results of Ansys, which shows that the positive bending stress in the mid-span cross-section of the main beam obtained by simplifying the main beam into a thin-walled deep beam is more close to the results of Ansys calculation. The results of this paper provide an important reference for the structural strength analysis of planar gates.

IDENTIFIKASI BAHAYA DAN PENILAIAN RISIKO DI KAWASAN WISATA LEUWI KENIT, CILETUH PALABUHANRATU UGG

Ciletuh Palabuhanratu as the first geopark in West Java which has been recognized by UNESCO since 2018, is famous as the first land in western Java. One of the natural tourist object in the Geopark area with the beauty of ancient rock structures aged more than 60 million years ago is the Leuwi Kenit natural tourist destination in Pasirpanjang Village, which has a very large number of tourists, but in certain periods there are often visitor accidents. This research aims to identify hazards and risk assessment, as well as risk control from hazards, with research objects including parking areas, entrance gates, access routes, play facilities, and exit routes. The research method is a qualitative Hazard Identification and Risk Assessment and mapping of danger points, literature studies, field observations, interviews with the community, tour guides and tourist attraction guards. Based on the results of the study, there are fifteen danger points in the Leuwi Kenit tourist attraction, some of which can occur when the activity is running with a range of risk relative status, namely low to high. Risk relative high status is recorded to have dominated with seven danger points, risk relative moderate status with six danger points, and risk relative low with two danger points. According to the results of the study, there are fifteen danger points in the Leuwi Kenit tourist attraction, some of which can occur when the activity is running with a range of risk relative status, namely low to high. Risk relative high status is recorded as dominant with seven danger points, risk relative moderate status with six danger points, and risk relative low status with two danger points. The results of the risk assessment show that the risk status is included in potential hazards with high and medium hazard risk levels, management attention and control planning are needed. Alternative risk controls that can be implemented to minimize the occurrence of risk are administrative, engineering, and elimination approaches. Forms of risk avoidance applications such as making paths according to safe standards, making information boards for hazard location points, and rearranging amusement ride according to safety standards at Leuwi Kenit.

Design And Analysis of Flapping Wing Aircraft Based on Crank Mechanism

This paper is proposed a flapping wing aircraft based on the crank slider mechanism to solve the problems of the two flapping wing structures, such as synchronization and excessive local stress common to existing ornithopters. MATLAB is used to solve the equations to determine the dimensions of the individual components, and the 3D model is designed by SolidWorks software. The static analysis on flapping wings, the static stress, and the static strain distribution map of flapping wings are carried out. Moreover, the mechanism of flapping wing aircraft is modeled in Adams software, which simulates the actual structure by designing the kinematic constraint relationships between the components. It was concluded that the flapping wing could achieve a flapping angle of 30 degrees in one cycle, which was consistent with the simulation results by MATLAB. Furthermore, it was found that the first principal stress of the danger point was less than the yield strength of the material to determine the rationality of material selection. Finally, the fluid trace distribution on the upper and lower sides of the flapping wings was analyzed, which was consistent with the actual situation.